Thermal switch



J1me 1953 P. GIUFFRIDA arm. 'I 2,643,311

" Tl-IERMAL SWITCH Filed June 22. 1951 INVENTORS P. G/UFFR/DA 3.5. SHAW BY 5am A TTOR/VEY Patented June 23, 1953 THERMAL SWITCH Philip Giuffrida, Lawrence, and Burton E. Shaw, East Boxford, Mass., assignors to Combustion Control Corporation, Cambridge, Mass., a corporation of Massachusetts Application June 22, 1951, Serial N0. 233,054

4 Claims. 1

This invention relates to a new and improved thermally actuated time delay switch which is especially suited for application as a safety switch in burner installations.

A principal object of this invention is to provide a mechanically and electrically reliable time delay switch of simple structure which can be easily and inexpensively fabricated.

It is contemplated that the switch structure of this invention may be utilized to advantage in conventional combustion control circuits wherein it is desired to operate safety apparatus, or initiate other operations, a timed interval after the failure of the burners of a furnace to operate in the proper manner. It should be understood, however, that the switch structure of this invention may be utilized to advantage in other applications wherein a delayed switching operation is desired.

The structure of a preferred embodiment of the novel switch herein described comprises a bimetal contact actuating element thermally coupled to a heater winding. A contact supporting arm is pivotally mounted to one end of said contact actuating element so that a force applied by a spring connected between said contact actuating element and said contact supporting arm will cause the contact supporting arm to move to the left or to the right, depending upon the positioning of the bimetal contact actuating element. In particular, if current flows through the heater winding for a sufiiciently long period of time, the bimetal contact actuating element will curve in a conventional manner causing the contact supporting arm to move the contacts thereon from a closed to a reset position. After the switch has operated in response to current flow through the heater winding, a manual operation of a reset plunger forces the contact supporting arm back to the closed position.

In order that all of the features of this invention and the mode of operation thereof may be readily understood, a detailed description is set forth hereinafter, with particular reference being made to the drawings, wherein:

Fig. 1 is a side elevational view of a preferred embodiment of the thermal switch of this invention, with a portion of the plunger casing in section, showing the transfer contact positioned in the closed position;

Fig. 2 is a side elevational view of the switch of Fig. 1, showing the transfer contact positioned in the reset position;

Fig. 3 is a side elevational View of the switch shown in Figs. 1 and 2, with a portion of the closed contact leaf and its supporting leaf re-- moved;

Fig.4 is a perspective View of the switch shown. in Figs. 1-3, with the contact supporting arm midway between the closed and reset positions;

Fig. 5 is an enlarged perspective View of the:

contact actuating mechanism shown in the previous figures.

Referring now to the drawings, and particularly to Figs. 1 and 2, the switch structure shown therein comprises two hemispherical ball contacts 5 rigidly fixed to ball contact supporting arm 6. The combination of ball contacts 5 and supporting arm 6 are pivotally mounted upon the upper bent portion of retaining piece I so that a single pole transfer function is provided by the two operative positions of contact 5 illustrated in Figs. 1 and 2. In particular, ball contact supporting arm 6 comprises a pair of mating teeth 8 projecting through a pair of slots located in the upper bent portion of retaining piece '1. Two pivot knees 9 are located adjacent the mating teeth whereby ball contacts 5 and their supporting arm 6 pivot about a sharp bottom edge of said knees so that contacts 5 can traverse easily from one operative position to the other.

The upper hooked portion of spring 10 is passed through a small hole in ball contact supporting arm 6, and the lower hooked portion of spring [0 is passed through a hole in the bottom hooked portion of metallic retaining piece 7 whereby a force is applied to ball contact supporting arm 6 which will cause said arm to move contacts 5 either to the left or to the right of the pivot edges of knees 9, as shown in Figs. 1 and 2, respectively.

Retaining piece I is mechanically coupled to bimetal actuating element H by a pair of rivets l2. Bimetal actuating element ll may be constructed of any conventional bimetal alloys so that the element curves to the left in response to an increase in ambient temperature. This curvature motion of actuating element II is not seriously impeded by metallic retaining piece I inasmuch as rivets l2 have the same vertical positioning near the upper edge of actuating element II and also because no other rivets in terconnect the two parts. For purposes of switch operation, heater winding [3 is thermally coupled to the body portion of actuating element H whereby said bimetal actuating element is caused to curve in the conventional manner in response to current flow through said heater winding.

Conductor M, which is soldered to ball con tact supporting arm 6 and retaining piece I, interconnects said components so that a low resistance electrical path is formed between ball contacts 5 and actuating element II. A reliable and low resistance electrical connection may therefore he made to ball contacts .5 by con;- necting a conductor to lug portion l5 of actu; ating element 1 I.

When ball contact supporting arm 6 is in the position shown in Fig. 1, left ball contact 5 rests against contact 16, which contact is mechanically coupled to bimetal contact leaf ll. When hall contact supporting arm 55 is in the p t'on shown in Fig. 2, right ball contact {a rests ag reset contact l8, which contact is mechanically coupled to metallic reset contact leaf l9 Contact leaf H is constructed of bimetal having the same temperature coefficient of curyature as actuating element ll. With such an arrangelas -i a arietie in hh hi hieerlsi ie iie due to current'flow through heater winding 13 will be compensated for inasmuch as contact leaf {Twill follow the curvature of actuating element I l. In'the usual embodiment, the metallic thiclig iies 9 leef enac IT is inadeq at to r vi uff ien i ehshi e siiepe e ehieei le a consequence, contact support leaf 20, with pivot mini .21 run -hes i the s er ortion there f is bieiiileil t iiie eiiieei y su ort Cont l ei 1 lifh s b n ie ihel that i ee ee sup t .2? is hieeheiiiee eeiihi ei lie e ie eaf I l by P e eeihi fishes i he i m e ei eeeiiieiehi .ei leiii've ir e eenieei l a is hei e he s as is d sires th m e a ure e m se i e th Ceniaetsiipeeri 2? is else asse s el t 'se xhe m el alloy used for th e trii ei Le sees l a '1 d" eeii i el me 1- hia ch a tem erat r eeiheehseii h is 11 q whe ht hel 90h s ,5 s n e es 1: e}; hewh i hi 2 i'ejs ehi et ea 8 vI. he ehsiili ilesi 9 sh materie W l h r l tde ie h eehehi sl p rt er e et e set l Iiisi lei eh i he' pre ents th ne h 'e .sh ri he o the m a h' l eile s .ef Ie RQ Wiii IJE i b hie i l e .e hieei eer 1.

The switch structure shown in the drawing provi es e e ii hs e swit h e ereii h heeeh ehi is '5 ma h Pesii h ee her ese h l e h: as I? e ese eehie S t e e e iriee eeh ee eh my e ii -s e e t w' i hi is s it' s 9i this s riieiii s by eentee w th the h ieih h s er ehs' i i; if she 39? .eehi i ee ii, i eiihs eieih h i and re t eehtiee i e l9 rle vei eh e i e i; t e her wiih ei i eiesi hs .ele he I lens reset cfitabtleaf l9 are mechanically spaced and e i e h' .iiisiiiei' e reih eiie anoth b iiisiiieiihs si se wh e s s s we iv i hei l e e ih r b s eei Phbi s ej essee he e finei heww is Pr id d the er iiehs 'e eii eei ee ii, epeer e .2 e i iih element l1, and reset contact leaf I3 between sei i e iieeers 24 so h i ee er belt 5 wil hei e e v e i sh r t ese o nt is ens eh- I The s a t ee e he i Z s el e e e-i 1 eh es e w t i h ii i iihe iihih ihei i sie ih ei essi eeaih ii e s hie jshere Hi Reeei Phih e i i eh hieel .si e i si b slipper iee 2 n h emhi eii i 'i iee 'i iiii l to l 'ih i eiih sp e r s 'eemh heiieh h hie-en r leeee t Bes i Pli hs r Z5 is Par ia l sii e ee iihi l n er esih 8- which casing is mechanically coupled to support eieee 2i Cem re sieh s r es 9 p iiPEfQWih' in casing 28 and shown in Fig. 1, applies a force to plunger 26 so that plunger push button 30 normally projects from the plunger casing 28 as shown in the drawings. Retaining ring 3| defines the maximum limit of the plunger push button projection.

The detailed description of the operation of the structure of this invention is as follows. Initially, contact supporting arm 6 and contacts 5 are in the position shown in Fig. 1, having been so'positioned by a' manual operation of plunger 29 in a manner hereinafter described in detail. l ball contact 5 is firmly positioned against contact I 6 by a downwardly directed force applied by spring 10 to contact supporting arm 6. In particular, inasmuch as this force is directed in a line which passes to the left of the pivot edges of knees 9, contacts 5 are rotated in a counterclockwise direction until they assume the position eheh ii isi- Th ehs e i hi m hi of s eei l a 1 s hi h 'm ed by e ea es e b se p essen issues w when If a potential source is applied to the terminal ehhee iehs i hea r i e o li thi time, eii iehi e iher h W 41 e eh-i' e t e ating element l I in a conventional rna nner and cause a bending curvature oi element tothe iei Whehihh wa i a se es greet; the force applied by spring lll't'o t support arm 5 will he directed me lineiw c now passes to'the right of thepiuot edges of kn'eesQ. "With s h' h ejeel eh f t' p-h h m 6' 11 ee i s ar ss l lekwis' th ab' 0:; tion 'ofth'e forceof spring ll} '1 right Balloon.- tact firfests against reset contact 1 2}: can ata"; and contact supper; v5 will'rnainta inthelreset es'iiie iil iei i e hei i h e h he subsequent termination of current a through i s e ieiheie e er eeh l i i s eenirol s ie: f y Operation, that electrical connection's'be ihede t h ss J le i 3 s0 th t i safety deli such as an audlhle alarm or frame ure saiei s are a sas n ll he .aei eie i i h eie t i' s i hes eh hi he w ieh lse s es:- longed heating Joy heater 7 ding 13'. There; s t s -he rese the s ii i i hiiii i pr s i hes i h s -We in hi ii is e es e i e n?- i eil ieii e e iih e hush sh -h men s has i s the? series ?9 Wi le e 'e s e whereb reset se ieceez e ii hsei' e' l i k ehe i eii l h i r s t eeh ee l i see ess suriace 3 3 of plunger tdwill mechanically bend cont t ieef 1 s ihei ht 2 es' i e l after, another reset operation {will be required to eeesii eh he suit Iii ,i sy e res ii aeh e ie e ir u e rtain conditions of higl i aifipierit ternperatiire, sufiicient curvature of .corrtalct actuating element ll ma eeee w iheiii' eiiiieh ie he ie winding [3 to actuate the switch from the position shown in Fig. 1 to the position shown in Fig. 2. To prevent such an occurrence, it is pref erable that contact leaf I! be constructed of the same bimetal alloy that was utilized in the construction of actuating element ii. With this arrangement, generally speaking, any increase in ambient temperature will cause a conventional displacement of both contact leaf ll and contact actuating element H so that the force applied by spring id will continue to be directed to the left of the pivot edges or knees 9. Consequently, the thermal switch of this invention is temperature compensated and may be actuated only by sustained current flow through heater winding l3.

It is to be understood that the above described arrangements are illustrative of the application of the principles of this invention. Numerous other arrangements may be devised by those skilled in the art without departing from the scope of this invention.

What is claimed is:

l. A thermally actuated time delay switch comprising a bimetallic contact actuating element having a heater winding thermally coupled thereto, a metallic retaining piece mechanically coupled to said contact actuating element, a contact supporting arm pivotally mounted upon the upper portion of said retaining piece, said contact supporting arm having a plurality of electrical contacts positioned thereon, a spring tensioned between said contact supporting arm and the lower portion of said retaining piece whereby the bending of said contact actuating element in response to thermal energy from said heater winding causes the line of direction of said spring force to reverse sides with respect to the pivot points of said contact supporting arm, and a plurality of contact leaves supporting stationary contacts disposed in a contact mating relationship with the contacts of said contact actuating element.

2. A thermally actuated time delay switch comprising a bimetallic contact actuating element having a heater winding thermally coupled thereto, a metallic retaining piece mechanically coupled to said contact actuating element, a contact supporting arm pivotally mounted upon the upper portion of said retaining piece, said contact supporting arm having a plurality of electrical contacts positioned thereon, a spring tensioned between said contact supporting arm and the lower portion of said retaining piece whereby the bending of said contact actuating element in response to thermal energy from said heater winding causes the line of direction of said spring force to reverse sides with respect to the pivot points of said contact supporting arm, a plurality of contact leaves supporting stationarycontacts disposed in a contact mating relationship with respect to the contacts of said contact actuating element, one of said contact leaves being constructed of the same bimetal used in the construction of said contact actuating element, and a reset plunger for applying a bending force to said plurality of contact leaves whereby one of the contacts of said contact supporting arm may be manually positioned against the mating contact of said bimetal contact leaf.

3. A thermally actuated time delay switch com- 7 prising a. bimetallic contact actuating element having a heater winding thermally coupled thereto, a metallic retaining piece mechanically coupled to said contact actuating element, a contact supporting arm pivotally mounted upon the upper portion of said retaining piece, said contact supporting arm having a plurality of electrical contacts positioned thereon, a spring tensioned between said contact supporting arm and the lower portion of said retaining piece whereby the bending of said contact actuating element in response to thermal energy from said heater winding causes the line of direction of said spring force to reverse sides with respect to the pivot points of said contact supporting arm, a plurality of contact leaves supporting stationary contacts disposed in a contact mating relationship with the contacts of said contact actuating element, one of said contact leaves being constructed of the same bimetal used in the construction of said contact actuating element, a bimetal supporting leaf applying a supporting force to said bimetal contact leaf through pivot means, and a reset plunger for applying a bending force to said plurality of contact leaves whereby one of the contacts of said contact supporting arm may be manually positioned against the mating contact of said bimetal contact leaf.

4. A thermally actuated time delay switch comprising a bimetallic contact actuating element having a heater winding thermally coupled thereto, a metallic retaining piece mechanically coupled to said contact actuating element and having an upper bent portion projecting at a substantially normal angle with respect to said contact actuating element and a lower hooked portion projecting through a hole in said contact actuating element, a contact supporting arm including a pair of pivot knees pivotally mounted upon the upper bent portion of said retaining piece, said contact supporting arm having a plurality of ball-type electrical contacts positioned thereon, a spring tensioned between said contact supporting arm and the lower hooked portion of said retaining piece whereby the bending of said contact actuating element in response to thermal energy from said heater winding causes the line of direction of said spring force to reverse sides with respect to the pivot points of said pivot knees, a plurality of contact leaves disposed in a parallel relationship with respect to said contact actuating element, each of said contact leaves having an electrical contact positioned thereon so as to mate with a difierent one of the contacts of said contact supporting arm, one of said contact leaves being constructed of the same bimetal used in the construction of said contact actuating element, a bimetal supporting leaf applying a supporting force to said bimetal contact leaf through pivot means, and a reset plunger for applying a bending force to said plurality of contact leaves whereby one of the contacts of said contact supporting arm may be manually positioned against the mating contact of, said bimetal contact leaf.

PHILIP GIUFFRIDA. BURTON E. SHAW.

References Cited in the file of this patent UNITED STATES PATENTS Number 

